关键词: 落叶松人工林, 农田, 土壤碳含量, 土壤氮含量, 理化性质

Abstract: Based on 8 paired plots in larch (Larix gmelinii) plantations and adjacent farmlands in northeast China, the aim of the present study is to find the relations of different soil layers vertical patterns to land uses. Seven out of the 8 paired samples showed higher SOC contents in surface (0-20 cm) soil of larch plantations than those in farmlands, and the mean value of the pooled data showed larch plantation was 37% higher. However, deeper soil layers showed a contrasting 8%-58% higher SOC contents in farmland. In different samples of SIC, higher SIC contents were observed in forest comparing with farmland in total 0-80 cm soil profile (forest: 1.33 mg·kg^-1; farmland: 1.17 mg·kg^-1 ). In most cases, surface (0-20 cm) soil layer of larch plantations showed higher soil N and alkaline-N content than those in farmland and the average increments of the 8 plots were respectively 20% and 34%. However, deeper layers (20-80 cm) usually showed contrasting tendencies. Higher soil N (6%) and alkaline N (4%) contents in farmland than those in forest land were found. Generally, 0-20 cm soil of forest had a higher pH, but lower EC and bulk density than those of farmland. In deep layers (20-80 cm), 4-5 of the 8 plots showed contrary patterns. Pooled data showed no obvious difference between these two land uses in pH, EC in farmlands was 2.2 μs·cm^-1 higher than forests, and bulk density showed a difference as small as 0.02 g·cm^-3(1%). These findings clearly manifested that the vertical pattern in soil C, N and other physic-chemical parameters is robustly evident, and land use impacts on surface soil may be totally different, and even contrary from those in deep layers. Without deep layer inclusion, some conclusions of SOC depletion and degradation of soil fertility by farmland reclamation may overestimate the changes and we should consider the changes both at surface and deep soils in future studies for a non-bias and scientific evaluation.

Key words: larch plantation, farmland, soil carbon content, soil nitrogen content, physicalchemical property